Cardiac rhythm management system selecting between multiple same-chamber electrodes for delivering cardiac therapy

ABSTRACT

A cardiac rhythm management system selects one of multiple electrodes associated with a particular heart chamber based on a relative timing between detection of a depolarization fiducial point at the multiple electrodes, or based on a delay between detection of a depolarization fiducial point at the multiple electrodes and detection of a reference depolarization fiducial point at another electrode associated with the same or a different heart chamber. Subsequent contraction-evoking stimulation therapy is delivered from the selected electrode.

TECHNICAL FIELD

The present system relates generally to cardiac rhythm managementsystems and particularly, but not by way of limitation, to such a systemselecting between multiple same-chamber electrodes for deliveringcardiac therapy.

BACKGROUND

When functioning properly, the human heart maintains its own intrinsicrhythm based on physiologically-generated electrical impulses. It iscapable of pumping adequate blood throughout the body's circulatorysystem. Each complete cycle of drawing blood into the heart and thenexpelling it is referred to as a cardiac cycle.

However, some people have abnormal cardiac rhythms, referred to ascardiac arrhythmias. Such arrhythmias result in diminished bloodcirculation. One mode of treating cardiac arrhythmias uses drug therapy.Drugs are often effective at restoring normal heart rhythms. However,drug therapy is not always effective for treating arrhythmias of certainpatients. For such patients, an alternative mode of treatment is needed.One such alternative mode of treatment includes the use of a cardiacrhythm management system. Such systems are often implanted in thepatient and deliver therapy to the heart.

Cardiac rhythm management systems include, among other things,pacemakers, also referred to as pacers. Pacers deliver timed sequencesof low energy electrical stimuli, called pace pulses, to the heart, suchas via an intravascular leadwire or catheter (referred to as a “lead”)having one or more electrodes disposed in or about the heart. Heartcontractions are initiated in response to such pace pulses (this isreferred to as “capturing” the heart). By properly timing the deliveryof pace pulses, the heart can be induced to contract in proper rhythm,greatly improving its efficiency as a pump. Pacers are often used totreat patients with bradyarrhythmias, that is, hearts that beat tooslowly, or irregularly. Such pacers may also coordinate atrial andventricular contractions to improve pumping efficiency.

Cardiac rhythm management systems also include defibrillators that arecapable of delivering higher energy electrical stimuli to the heart.Such defibrillators also include cardioverters, which synchronize thedelivery of such stimuli to portions of sensed intrinsic heart activitysignals. Defibrillators are often used to treat patients withtachyarrhythmias, that is, hearts that beat too quickly. Such too-fastheart rhythms also cause diminished blood circulation because the heartisn't allowed sufficient time to fill with blood before contracting toexpel the blood. Such pumping by the heart is inefficient. Adefibrillator is capable of delivering a high energy electrical stimulusthat is sometimes referred to as a defibrillation countershock, alsoreferred to simply as a “shock.” The countershock interrupts thetachyarrhythmia, allowing the heart to reestablish a normal rhythm forthe efficient pumping of blood. In addition to pacers, cardiac rhythmmanagement systems also include, among other things,pacer/defibrillators that combine the functions of pacers anddefibrillators, drug delivery devices, and any other implantable orexternal systems or devices for diagnosing or treating cardiacarrhythmias.

One problem faced by physicians treating cardiovascular patients is thetreatment of congestive heart failure (also referred to as “CHF”).Congestive heart failure, which can result from long-term hypertension,is a condition in which the muscle in the walls of at least one of theright and left sides of the heart deteriorates. By way of example,suppose the muscle in the walls of left side of the heart deteriorates.As a result, the left atrium and left ventricle become enlarged, and theheart muscle displays less contractility. This decreases cardiac outputof blood through the circulatory system which, in turn, may result in anincreased heart rate and less resting time between heartbeats. The heartconsumes more energy and oxygen, and its condition typically worsensover a period of time.

In the above example, as the left side of the heart becomes enlarged,the intrinsic electrical heart signals that control heart rhythm mayalso be affected. Normally, such intrinsic signals originate in thesinoatrial (SA) node in the upper right atrium, traveling throughelectrical pathways in the atria and depolarizing the atrial hearttissue such that resulting contractions of the right and left atria aretriggered. The intrinsic atrial heart signals are received by theatrioventricular (AV) node which, in turn, triggers a subsequentventricular intrinsic heart signal that travels through specificelectrical pathways in the ventricles and depolarizes the ventricularheart tissue such that resulting contractions of the right and leftventricles are triggered substantially simultaneously.

In the above example, where the left side of the heart has becomeenlarged due to congestive heart failure, however, the conduction systemformed by the specific electrical pathways in the ventricle may beaffected, as in the case of left bundle branch block (LBBB). As aresult, ventricular intrinsic heart signals may travel through anddepolarize the left side of the heart more slowly than in the right sideof the heart. As a result, the left and right ventricles do not contractsimultaneously, but rather, the left ventricle contracts after the rightventricle. This reduces the pumping efficiency of the heart. Moreover,in LBBB, for example, different regions within the left ventricle maynot contract together in a coordinated fashion.

For these and other reasons, there is a need to provide cardiac rhythmmanagement therapy that coordinates the timing of contractions ofdifferent sides of the heart, and/or alters the conduction of adepolarization through a single chamber of the heart to improve theefficiency of a contraction associated with that heart chamber.

SUMMARY

This document discusses a cardiac rhythm management system that selectsone of multiple electrodes associated with a particular heart chamber.Subsequent contraction-evoking stimulation therapy is delivered from theselected electrode. Both methods and apparatuses are discussed.

In one embodiment, the electrode is selected based on a relative timingbetween detection of a same fiducial point of a cardiac depolarizationat the multiple electrodes. The electrode that is last to detect thefiducial point is selected for subsequent delivery ofcontraction-evoking stimulations.

In another embodiment, a reference first chamber depolarization fiducialpoint is detected. A second chamber depolarization fiducial point isdetected at each of multiple second chamber electrodes during the samecardiac cycle as the reference fiducial point. Time intervals aremeasured between the reference fiducial point and each of the secondchamber fiducial points. The electrode corresponding to the longest suchtime interval is selected for subsequent delivery of contraction-evokingstimulations.

In a further embodiment, a first depolarization fiducial point isdetected from the first heart chamber. During the same cardiac cycle, asecond depolarization point is detected from a first electrodeassociated with the second heart chamber. A first time interval ismeasured between the first and second fiducial points. During asubsequent cardiac cycle, a third fiducial point, of the same nature asthe first fiducial point, is detected from the first heart chamber.During the same cardiac cycle, a fourth fiducial point, of the samenature as the second fiducial point, is detected from a second electrodeassociated with the second heart chamber. A second time interval ismeasured between the third and fourth fiducial points. The electrodecorresponding to the longer of the first and second time intervals isselected for subsequent delivery of contraction-evoking stimulations.

In yet a further embodiment, a reference fiducial point is detected,over one or more cardiac cycles, from one of a plurality of electrodesassociated with a heart chamber. During the one or more cardiac cycles,corresponding fiducial points associated with heart depolarizations aredetected at the electrodes, and time intervals are measured between theheart depolarization fiducial points and the respective referencefiducial points. The electrode associated with the longest time intervalis used for subsequent delivery of stimulations. Other aspects of thepresent system and methods will become apparent upon reading thefollowing detailed description of the invention and viewing the drawingsthat form a part thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsdescribe substantially similar components throughout the several views.Like numerals having different letter suffixes represent differentinstances of substantially similar components. The drawings illustrategenerally, by way of example, but not by way of limitation, variousembodiments discussed in the present document.

FIG. 1 is a schematic/block diagram illustrating generally, among otherthings, one embodiment of portions of a cardiac rhythm management systemand an environment in which it is used.

FIG. 2 is a graph illustrating generally, among other things, onetechnique of selecting between multiple electrodes associated with thesame heart chamber.

FIG. 3 is a graph illustrating generally, among other things, atechnique of acquiring data over a plurality of cardiac cycles forselecting between multiple electrodes associated with the same heartchamber.

FIG. 4 is a schematic/block diagram illustrating generally, among otherthings, another embodiment of portions of a cardiac rhythm managementsystem and an environment in which it is used.

FIG. 5 is a graph illustrating generally, among other things, anothertechnique of selecting between multiple electrodes associated with thesame heart chamber.

FIG. 6 is a graph illustrating generally, among other things, anothertechnique of selecting between multiple electrodes associated with thesame heart chamber, using time intervals obtained during differentcardiac cycles.

FIG. 7 is a graph example of selecting one of electrodes associated withthe same heart chamber using time intervals measured from a referencefiducial point obtained from one of the same electrodes associated withthat heart chamber.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments or examples. These embodimentsmay be combined, other embodiments may be utilized, and structural,logical and electrical changes may be made without departing from thespirit and scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the present invention is defined by the appended claims andtheir equivalents.

The present methods and apparatus are described with respect toimplantable cardiac rhythm management (CRM) devices, such as pacemakers,cardioverter/defibrillators, pacer/defibrillators, and multi-chamberand/or multi-site (in a single or multiple heart chambers) cardiacresynchronization therapy (CRT) devices. Such CRT devices are includedwithin CRM devices even though the CRT devices need not necessarilymodulate heart rate. Such CRT devices may instead providecontraction-evoking stimulations that establish or modify the conductionpath of propagating depolarizations to obtain more efficient pumping ofthe heart. Moreover, the present methods and apparatus also findapplication in other implantable medical devices, and in unimplanted(external) devices, including, but not limited to, external pacemakers,cardioverter/defibrillators, pacer/defibrillators, multi-chamber and/ormulti-site CRT devices, monitors, programmers and recorders, whethersuch devices are used for providing a diagnostic, a therapy, or both.

FIG. 1 is a schematic/block diagram illustrating generally oneembodiment of portions of the present cardiac rhythm management system100 and an environment in which it is used. In this embodiment, system100 includes, among other things, cardiac rhythm management device 105,which is coupled by leads 110A-B to heart 115. Heart 115 includes fourchambers: right atrium 115A, right ventricle 115B, left atrium 115C, andleft ventricle 115D. Heart 115 also includes a coronary sinus 115E, avessel that extends from right atrium 115A toward the left ventricularfree wall, and which, for the purpose of this document, is considered toinclude the great cardiac vein and/or tributary vessels.

In one embodiment, lead 110A includes an electrode associated with rightatrium 115A, such as tip electrode 120 and/or ring electrode 125. Theelectrode is “associated” with the particular heart chamber by insertingit into that heart chamber, or by inserting it into a portion of theheart's vasculature that is close to that heart chamber, or byepicardially placing the electrode outside that heart chamber, or by anyother technique of configuring and situating an electrode for sensingsignals and/or providing therapy with respect to that heart chamber.Lead 110B, which is introduced into coronary sinus 115E and/or the greatcardiac vein or one of its tributaries, includes one or a plurality ofelectrodes associated with left ventricle 115D, such as electrodes 130and 135. Device 105 may also include other electrodes, such as housingelectrode 150 and/or header electrode 155, which are useful for, amongother things, unipolar sensing of heart signals or unipolar delivery ofcontraction-evoking stimulations in conjunction with one or more of theelectrodes 120, 125, 130, and 135 associated with heart 115.Alternatively, bipolar sensing and/or therapy may be used betweenelectrodes 120 and 125, between electrodes 130 and 135, or between oneof electrodes 130 and 135 and another closely situated electrode.

Device 105 includes a sensing module 160, which is coupled to one ormore of the electrodes for sensing electrical depolarizationscorresponding to heart chamber contractions. Such electricaldepolarizations of the heart tissue include atrial depolarizations,referred to as P-waves, and ventricular depolarizations, referred to asQRS complexes. The QRS complex is a rapid sequence of several signalexcursions away from a baseline in sequentially switching polarity, withthe largest excursion referred to as an R-wave. Peak detector 165 iscoupled to sensing module 160 for detecting the P-wave peak from rightatrium 115A, obtained by bipolar sensing between electrodes 120 and 125or by any other sensing technique. Peak detector 165 also senses theR-wave peak at a plurality of different sites associated with leftventricle, such as at each of electrodes 130 and 135. In one example,electrode 130 is located near the left ventricular apex and electrode135 is located near the left ventricular base region, i.e., closer tothe left atrium 115C. In another example, one of these two electrodes130 and 135 (or an additional third electrode) is located in a middleportion (“midregion”) of left ventricle 115D between the leftventricular apex and the left ventricular base region. In anotherexample, electrodes 130 and 135 are located in a middle cardiac vein andcloser to a septum region. The electrodes are located either on the freewall and/or the anterior wall of the ventricle. Sensing at electrodes130 and 135 is either unipolar (e.g., the electrode 130 and/or 135 issensed in combination with a relatively distant electrode, such as oneor both of housing electrode 150 and/or header electrode 155) or bipolar(e.g., the electrode 130 and/or 135 is sensed in combination withanother relatively close electrode, such as another electrode disposedon lead 110B and associated with left ventricle 115D, or anotherelectrode disposed on lead 110A and associated with right atrium 115A).System 100 also includes a telemetry transceiver 185 in device 105,which is communicatively coupled to an external programmer 190.

FIG. 1, and the graph of FIG. 2, illustrates an embodiment in whichtimer 170 measures a first right atrium to left ventricle (RA-LV) timeinterval between the detection of an intrinsic P-wave at time t₀ atelectrode 120 and the subsequent detection during the same cardiac cycleof an intrinsic R-wave peak at time t₁ at first left ventricularelectrode 130. A cardiac cycle includes both an atrial and the resultingventricular heart contraction, and may be measured between P-waves,between R-waves, or between any other fiducial points on a heart signal,where the fiducial point occurs once per cardiac cycle. Timer 170 alsomeasures a second RA-LV time interval between the detection of theintrinsic P-wave at time t₀ at electrode 120 and the subsequentdetection during the same cardiac cycle of an intrinsic R-wave peak attime t₂ at a second left ventricular electrode 135. Controller 175 iscoupled to timer 170 to receive these first and second time intervals(t₁−t₀) and (t₂ t₀), respectively.

Based on a comparison between these time intervals, controller 175selects one of electrodes 130 and 135 to which therapy module 180 iscoupled for delivering subsequent contraction-evoking stimulationtherapy to left ventricle 115D. In this example, controller 175 selectsthe one of electrodes 130 and 135 that corresponds to a longer detectedtime interval between the detection of the P-wave associated with theright atrium 115A and the detection of the R-wave associated with leftventricle 115D. Thus, if (t₁−t₀)>(t₂−t₀), then electrode 130 is selectedfor delivering contraction-evoking stimulations. If (t₁−t₀)<(t₂−t₀),then electrode 135 is selected for delivering contraction-evokingstimulations. If (t₁−t₀)=(t₂−t₀), then, in one example, the electrodethat is closest to the apex of heart 115 (e.g., electrode 130) isselected for delivering contraction-evoking stimulations. In a furtherexample, a threshold time difference, Δt, is used for making thecomparison. In this example, if (t₁−t₀)>[(t₂−t₀)+Δt], then electrode 130is selected for delivering stimulations. If [(t₁−t₀)+Δt]<(t₂−t₀), thenelectrode 135 is selected for delivering stimulations. Otherwise,electrode 130, or other electrode closest to the apex of heart 115, isselected for delivering stimulations. In one example, Δt isapproximately between 0 milliseconds and 20 milliseconds inclusive, suchas about 10 milliseconds. In a further example, an indication of whichof electrodes 130 and 135 was selected is communicated from device 105by transceiver 185 to external programmer 190 for display to a user.

In an alternate embodiment, the reference time t₀ is not used, but therelative times t₁ and t₂ are instead compared directly. If t₁>t₂, thenelectrode 130 is selected for delivering contraction-evokingstimulations, if t₁<t₂, then electrode 135 is selected for deliveringcontraction-evoking stimulations, if t₁=t₂, then electrode 130, or otherelectrode closest to the apex of heart 115, is selected for deliveringcontraction-evoking stimulations. In a further example, a threshold timedifference, Δt, is used for making the comparison. For example, ift₁>(t₂+Δt), then electrode 130 is selected for delivering stimulations,if (t₁+Δt)<t₂, then electrode 135 is selected for deliveringstimulations, otherwise electrode 130, or other electrode closest to theapex of heart 115, is selected for delivering stimulations.

In another alternate embodiment, a reference time is used, but thisreference time and the times t₁ and t₂ are measured during differentcardiac cycles. During a first cardiac cycle, a P-wave is detected atelectrode 120 at time t_(0A) and an R-wave is detected at electrode 130at time t₁, and a time interval (t₁−t_(0A)) is measured based on thesedetections. During a second cardiac cycle, another P-wave is detected atelectrode 120 at time t_(0B), and an R-wave is detected at electrode 135at time t₂, and a time interval t₂−t_(0B) is measured. The timeintervals (t₁−t_(0A)) and (t₂−t_(0B)) are then compared, as discussedabove, for selecting one of electrodes 130 and 135 for deliveringstimulations.

In another alternate embodiment, a left atrial (LA) electrode issubstituted for the right atrial electrode 120, and LA-LV time intervalsare measured at each of the LV electrodes 130 and 135.

FIG. 3 is a graph illustrating generally another embodiment in which theP-R time intervals of interest are evaluated over a plurality of cardiaccycles for determining which of electrodes 130 and 135 to select fordelivering therapy. In one example, a statistic, such as an average (ormedian or otherwise lowpass filtered value) over n consecutive ornonconsecutive intrinsic cardiac cycles, is computed for the P-R1intervals detected between electrode 130 and electrode 120, and for theP-R2 intervals detected between electrode 135 and electrode 120. If theaverage P-R1 interval exceeds the average P-R2 interval, eitherabsolutely or alternatively by a predetermined threshold time Δt, thenelectrode 130 is selected for delivering subsequent contraction-evokingstimuli. If the average P-R2 interval exceeds the average P-R1 interval,either absolutely or alternatively by a predetermined threshold time Δt,then electrode 135 is selected for delivering subsequentcontraction-evoking stimuli. If the average P-R2 interval is equal tothe average P-R1 interval, or alternatively the difference between theseaverage intervals is less than or equal to the threshold time Δt, thenthe electrode closest to the apex of heart 115, such as electrode 130,is selected for delivering subsequent contraction-evoking stimuli.

In one embodiment, after such therapy is delivered over several cardiaccycles, then the therapy is occasionally or periodically (e.g., hourly,daily, monthly) turned off (either automatically or manually) for againperforming one of the techniques described herein to determine which ofelectrodes 130 and 135 to provide therapy from during a subsequent timeperiod.

Similar statistical techniques are used in an embodiment in which theselection of one of electrodes 130 and 135 for deliveringcontraction-evoking stimulations is based on the relative time ofoccurrence of depolarization fiducial points at electrodes 130 and 135,without using a reference point such as the P-wave. In one such example,the depolarization fiducial point is detected at both electrodes 130 and135 over several consecutive or nonconsecutive cardiac cycles. If, onaverage, the depolarization fiducial point (e.g., R-wave peak) of agiven cardiac cycle is detected at electrode 130 before it is detectedat electrode 135, then electrode 135 is selected for deliveringsubsequent contraction-evoking stimulations, otherwise, electrode 130 isselected for delivering subsequent contraction-evoking stimulations. If,on average, the depolarization fiducial point (e.g., R-wave peak) of agiven cardiac cycle is detected at electrode 130 at the same time thatit is detected at electrode 135, then the electrode that is closest tothe apex of heart 115, such as electrode 130, is selected. Moreover,such comparisons may use a threshold time such as discussed above.

FIG. 4 is a schematic/block diagram of one alternate embodimentincluding right ventricular electrodes, such as tip electrode 400 andring electrode 405. FIG. 4, and the graph of FIG. 5, illustrates anembodiment in which timer 170 measures a first right ventricle to leftventricle (RV-LV) time interval between the detection of an intrinsicR-wave peak at time t₀ at right ventricular electrode 400 and thesubsequent detection during the same cardiac cycle of an intrinsicR-wave peak at time t₁ at first left ventricular electrode 130. Timer170 also measures a second RV-LV time interval between the detection ofthe intrinsic R-wave peak at time t₀ at right ventricular electrode 400and the subsequent detection during the same cardiac cycle of anintrinsic R-wave peak at time t₂ at a second left ventricular electrode135. Controller 175 is coupled to timer 170 to receive these first andsecond time intervals (t₁−t₀) and (t₂−t₀), respectively.

Based on a comparison between these time intervals, controller 175selects one of electrodes 130 and 135 to which therapy module 180 iscoupled for delivering subsequent contraction-evoking stimulationtherapy to left ventricle 115D. In this example, controller 175 selectsthe one of electrodes 130 and 135 that corresponds to a longer detectedRV-LV time interval between the detection of the R-wave associated withthe right ventricle 115B and the detection of the R-wave associated withleft ventricle 115D. Thus, if (t₁−t₀)>(t₂−t₀), then electrode 130 isselected for delivering contraction-evoking stimulations. If(t₁−t₀)<(t₂−t₀), then electrode 135 is selected for deliveringcontraction-evoking stimulations. If (t₁−t₀)=(t₂−t₀), then the electrodeclosest to the heart apex, such as electrode 130, is selected fordelivering contraction-evoking stimulations. As discussed above, in afurther example, a threshold time difference, Δt, is used for making thecomparison. Thus, if (t₁−t₀)>[(t₂−t₀)+Δt], then electrode 130 isselected for delivering stimulations. If [(t₁−t₀)+Δt]<(t₂−t₀), thenelectrode 135 is selected for delivering stimulations. Otherwise theelectrode closest to the heart apex, such as electrode 130, is selectedfor delivering stimulations.

As discussed above, the time intervals (t₁−t₀) and (t₂−t₀) need not bemeasured during the same cardiac cycle, as illustrated in the graph ofFIG. 6. In the example of FIG. 6, a time interval (t₁−t_(0A)) ismeasured during a first cardiac cycle and a time interval (t₂−t_(0B)) ismeasured during a second (consecutive or nonconsecutive) cardiac cycle.In this example, if (t₁−t_(0A))>(t₂−t_(0B)), then electrode 130 isselected for delivering contraction-evoking stimulations. If(t₁−t_(0A))<(t₂−t_(0B)), then electrode 135 is selected for deliveringcontraction-evoking stimulations. If (t₁−t_(0A))=(t₂−t_(0B)), then theelectrode that is closest to the apex of heart 115, such as electrode130, is selected for delivering contraction-evoking stimulations. In afurther example, as discussed above, a threshold time difference, Δt, isused for making the comparison. Thus, if (t₁−t_(0A))>[(t₂−t_(0B))+Δt],then electrode 130 is selected for delivering stimulations. If[(t₁−t_(0A))+Δt]<(t₂−t_(0B)), then electrode 135 is selected fordelivering stimulations. Otherwise, the electrode closest to the heartapex, such as electrode 130, is selected for delivering stimulations. Bymeasuring the time intervals during different cardiac cycles, a singlesense amplifier can be multiplexed between electrodes 130 and 135 fordetecting the depolarization fiducial points. In certain embodiments,this advantageously allows for reduced circuitry. Although FIG. 6illustrates an embodiment in which a right ventricular depolarizationfiducial point is used as a reference point for measuring the timeintervals, such techniques for measuring time intervals separatelyduring different cardiac cycles is equally applicable to the othertechniques discussed herein using other fiducial points.

Moreover, as discussed above, with respect to FIG. 3, in a furtherembodiment, data is acquired over a plurality of cardiac cycles, and astatistical comparison of RV-LV time intervals, with or without using Δtfor the comparison, is used to select the particular LV electrode fordelivering contraction-evoking stimulations. In one embodiment, thesubsequent contraction-evoking stimulation therapy is delivered withoutcorresponding contraction-evoking stimulations delivered to rightventricle 115B. However, in another embodiment, each subsequentcontraction-evoking stimulation therapy delivered by the selected one ofleft ventricular electrodes 130 and 135 is accompanied by acorresponding appropriately timed stimulation delivered by rightventricular electrode 400. This is referred to as biventricular cardiacresynchronization therapy. The stimulation delivered at the selected oneof left ventricular electrodes 130 and 135 may be simultaneous to, ordifferent from, the time of the corresponding stimulation delivered byright ventricular electrode 400.

FIG. 7 is a graph example of selecting one of the electrodes associatedwith the same heart chamber, such as left ventricle 115D, using timeintervals measured from a reference fiducial point obtained from one ofthe same electrodes associated with that heart chamber. In this example,a reference fiducial point is obtained at time t_(0A) by the first oneof LV electrodes 130 and 135 to detect an onset of a QRS complex. Thisonset of the QRS complex, which is referred to as Q*, serves as thereference fiducial point. One example of detecting Q* is discussed inDing et al. U.S. Pat. No. 6,144,880, entitled “Cardiac Pacing UsingAdjustable Atrio-Ventricular Delays,” assigned to Cardiac Pacemakers,Inc., the entirety of which is incorporated herein by reference. TheR-wave peak, or other fiducial point associated with a QRS complex, isdetected at time t₁ at electrode 130. A first time difference t₁−t_(0A)is measured. In this example, the same reference fiducial point is againdetected, during a subsequent consecutive or nonconsecutive cardiaccycle, at time t_(0B) by the first one of LV electrodes 130 and 135 todetect Q*. The R-wave peak, or the other fiducial point similar to thefiducial point measured from electrode 130 at time t₁, is detected attime t₂ at electrode 135. A second time difference t₂−t_(0B) ismeasured. In this example, if (t₁−t_(0A))>(t₂−t_(0B)), then electrode130 is selected for delivering contraction-evoking stimulations. If(t₁−t_(0A))<(t₂−t_(0B)), then electrode 135 is selected for deliveringcontraction-evoking stimulations. If (t₁−t_(0A))=(t₂−t_(0B)), then theelectrode closest to the apex of heart 115, such as electrode 130, isselected for delivering contraction-evoking stimulations. In a furtherexample, as discussed above, a threshold time difference, Δt, is usedfor making the comparison. Thus, if (t₁−t_(0A))>[(t₂−t_(0B))+Δt], thenelectrode 130 is selected for delivering stimulations. If[(t₁−t_(0A))+Δt]<(t₂−t_(0B)), then electrode 135 is selected fordelivering stimulations. Otherwise, the electrode closest to the heartapex, such as electrode 130, is selected for delivering stimulations.Although the example illustrated in FIG. 7 relates to using multiplecardiac cycles, it is understood that this technique could be carriedout during a single cardiac cycle using a single reference point tosubstituted for the above reference points t_(0A) and t_(0B). Moreover,because Q* typically occurs substantially simultaneously at multipleelectrodes associated with the same heart chamber, the Q* referencefiducial point can typically be detected from any one of the multipleelectrodes associated with the same heart chamber.

FIGS. 1-6 illustrate that selecting the particular electrode, from aplurality of electrodes associated with left ventricle 115D, is in oneembodiment based on the longer RA-LV measurement, and in anotherembodiment is based on the longer RV-LV measurement. In a furtherembodiment, selecting the particular electrode from a plurality ofelectrodes associated with the same ventricle is based on a timemeasurement from any selected reference fiducial point associated withany heart chamber to any other selected fiducial point associated withdetection at the electrodes of one depolarization of that ventricle. Onesuch example is illustrated in FIG. 7, in which a first left ventricularelectrode detects a Q* fiducial point, then the second left ventricularelectrode also detects the Q* fiducial points. Thus, the plurality ofventricular electrodes each detect the same type of fiducial pointassociated with the ventricular heart contraction. For example, if afirst left ventricular electrode detects the R-wave peak, then thesecond left ventricular electrode also detects the R-wave peak. Inanother embodiment, if the first left ventricular electrode detects thepoint of maximum slope associated with a left ventricular R-wave, thenthe second left ventricular electrode also detects the point of maximumslope associated with the left ventricular R-wave. Stated differently,the left ventricular fiducial points are substantially similarly locatedon received heart depolarizations or, alternatively, may be located atdifferent portions of the heart depolarization signal if the expectedtime interval between these different locations is known. FIGS. 1-6particularly describe using P-wave and R-wave peaks as fiducial points,however, other examples of possible fiducial points include, among otherthings, a point of minimum slope on the detected heart signals.Moreover, as discussed above, the relative timing of the fiducial pointdetected at each same-chamber electrode can be compared directly,without using a reference fiducial point to establish corresponding timeintervals as discussed above with respect to certain embodiments.

Moreover, in an alternative embodiment, for a heart 115 in which theelectrical pathways cause the left ventricle to contract before theright ventricle, a left ventricular to right ventricular (LV-RV) delayis measured at a plurality of right ventricular electrodes, andsubsequent contraction-evoking stimulations are delivered from thatright ventricular electrode corresponding to the longest LV-RV delay.Thus, in a broader sense, a particular electrode from a plurality ofelectrodes associated with a first ventricle is selected for subsequenttherapy delivery based on that electrode having a later detecteddepolarization than the other electrodes in the plurality of electrodes.In a further embodiment, system 100 not only selects between multipleelectrodes associated with the same heart chamber, but also selectsbetween right ventricle 115B and left ventricle 155D for delivering thecontraction-evoking stimulations, such as described in Ding et al. U.S.patent application Ser. No. 09/738,407, assigned to Cardiac Pacemakers,Inc., the disclosure of which is incorporated herein by reference in itsentirety.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments may be used in combination with each other. Many otherembodiments will be apparent to those of skill in the art upon reviewingthe above description. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled. In the appendedclaims, the terms “including” and “in which” are used as theplain-English equivalents of the respective terms “comprising” and“wherein.”

What is claimed is:
 1. A method including: detecting a first fiducialpoint, associated with a first heart depolarization, at a firstelectrode associated with a first heart chamber; detecting the firstfiducial point, associated with the first heart depolarization, at asecond electrode associated with the first heart chamber; determining atime of the detection of the fist fiducial point at the first electrodeand a time of the detection of the first fiducial point associated withthe second electrode; selecting the first electrode if the firstfiducial point is detected at the second electrode before the firstfiducial point is detected at the first electrode, and selecting thesecond electrode if the first fiducial point is detected at the firstelectrode before the first fiducial point is detected at the secondelectrode; and delivering from the selected electrode a subsequentstimulation for evoking a contraction of the first heart chamber.
 2. Themethod of claim 1, in which the first heart chamber is a ventricle,selected from a left ventricle and a right ventricle, and the firstheart depolarization is a QRS complex associated with one contraction ofthe ventricle.
 3. The method of claim 2, in which the first fiducialpoint is associated with a peak of an R-wave in the QRS complex.
 4. Themethod of claim 2, further including disposing the first electrode atone of a base, midregion, and apex of a free wall of the ventricle, anddisposing the second electrode at a different one of the base,midregion, and apex of the free wall of the ventricle.
 5. The method ofclaim 1, in which selecting includes selecting the first electrode if,over a plurality of cardiac cycles, the first fiducial point isstatistically detected at the second electrode before the first fiducialpoint is statistically detected at the first electrode, and selectingthe second electrode if, over the plurality of cardiac cycles, the firstfiducial point is statistically detected at the first electrode beforethe first fiducial point is statistically detected at the secondelectrode.
 6. The method of claim 5, in which selecting further includesselecting one of the first and second electrodes located closer to aheart apex if the first fiducial point is statistically detected at bothof the first and second electrodes at substantially the same time. 7.The method of claim 1, further including repeating the steps of claim 1after a plurality of cardiac cycles.
 8. The method of claim 1, in whichselecting includes selecting one of the first and second electrodes thatis closer to a heart apex if the first fiducial point is detected atboth of the first and second electrodes at substantially the same time.9. The method of claim 1, in which selecting includes selecting thefirst electrode if the first fiducial point is detected at the secondelectrode before, by at least a threshold time, the first fiducial pointis detected at the first electrode, and selecting the second electrodeif the first fiducial point is detected at the first electrode before,by at least the threshold time, the first fiducial point is detected atthe second electrode.
 10. The method of claim 1, in which determiningthe timing includes: detecting at least one reference fiducial point;measuring first and second time intervals between the at least onereference fiducial point and the first fiducial point detected at therespective first and second electrodes; and comparing the first andsecond time intervals.
 11. A system including: first and secondelectrodes, both configured to be associated with a first heart chamber;a sensing circuit, coupled to the first and second electrodes, thesensing circuit detecting heart depolarizations associated with thefirst heart chamber, including detecting a first depolarization time atwhich a first depolarization of the first heart chamber is received atthe first electrode, and detecting a second depolarization time at whichthe first depolarization of the first heart chamber is received at thesecond electrode; a therapy circuit delivering stimulations for evokingheart contractions from at least one of the first and second electrodes;and a controller, coupled to the sensing circuit, the controllerselecting the second electrode if the first depolarization time occursbefore the second depolarization time, and selecting the first electrodeif the second depolarization time occurs before the first depolarizationtime, the controller coupling the therapy circuit to the selected one ofthe first and second electrodes for delivering the stimulations.
 12. Thesystem of claim 11, in which the first and second electrodes areconfigured to be associated with a ventricle selected from a groupconsisting of a left ventricle and a right ventricle.
 13. The system ofclaim 11, in which the sensing circuit provides, over a plurality ofcardiac cycles, a plurality of first depolarization times and aplurality of second depolarization times, and the controller computes afirst statistic associated with the plurality of first depolarizationtimes and a second statistic associated with the plurality of seconddepolarization times, and the controller selects one of the first andsecond electrodes by comparing the first and second statistics, and thecontroller couples the therapy circuit to the selected one of the firstand second electrodes for delivering the stimulations.
 14. The system ofclaim 13, in which the controller selects the first electrode if thesecond depolarization times statistically occur before the firstdepolarization times and selects the second electrode if the firstdepolarization times statisically occur before the second depolarizationtimes.
 15. The system of claim 14, in which the controller selects oneof the first and second electrodes that is located closer to a heartapex if the first and second depolarization times statisically occur atapproximately the same time.
 16. The system of claim 11, in which thecontroller selects the first electrode if the second depolarizationoccurs before the first depolarization by a predetermined thresholdtime, selects the second electrode if the first depolarization occursbefore the second depolarization by the predetermined threshold time,and otherwise selects one of the first and second electrodes locatedcloser to a heart apex.
 17. The system of claim 11, in which after thetherapy circuit delivers stimulations from the selected one of the firstand second electrodes over a plurality of cardiac cycles, the controlleragain selects one of the first and second electrodes for then couplingthe therapy circuit to the selected one of the first and secondelectrodes for delivering the stimulations.
 18. The system of claim 11,further including a remote programmer communicatively coupled to thecontroller, the controller including an indication of which of the firstand second electrodes is selected for delivering the stimulations, andthe programmer capable of receiving the indication from the controller.